Answer:
The two neighboring planets with the greatest distance between them is Neptune and Uranus. This happens when they are at the opposite sides of the Sun at approximately. They are 4500 million miles away from each other.
If by adjacent you mean next to each other, in terms of the order of planets in our Solar System, then the closest would be Earth and Venus; which are separated by about 38,000,000 kilometres when in opposition.
I am not sure about the general patterns..
Venus has the longest day of any planet in our solar system. It completes one rotation every 243 Earth days.
A year on Neptune is the longest of any planet, lasting the equivalent of 164.8 years (or 60,182 Earth days). It is obvious because it is also the farthest with the longest orbit.
Outer planets are less dense than the inner planets because they posses a big volume but contains not much mass. Try to imagine 2 rocks, one is big, but is hollow or have a lot of holes; and the other is small, but solid with no holes.
Happy learning!!
